If Polly is built with LLVM_POLLY_LINK_INTO_TOOLS=ON (the default for
monorepo builds), then Polly will become a dependency of the
LLVMExtensions component, which is part of LLVMExports. As such, all the
Polly libraries also have to be part of LLVMExports.
However, if Polly is built with LLVM_POLLY_LINK_INTO_TOOLS=OFF, we also
end up adding Polly libraries to LLVMExports. This is undesirable, as it
adds a hard dependency from llvm on polly.
Fix this by only exporting polly libraries from LLVMExports if
LLVM_POLLY_LINK_INTO_TOOLS is enabled.
2d6d476ffb